Arc extinguisher containing molybdenum disulfide



Nov. 19, 1963 .1. w. STEWART ETAL 3,111,557

ARC EXTINGUISHER CONTAINING MOLYBDENUM DISULFIDE Filed Nov. 15, 1962 INVENTORS J05 W. STEWART BY CHARLES E. BULLOCH Robert L. Lindgren Affomvsv United States Patent Ofiice 3,111,567 Patented Nov. 19, 1963 3,111,567 ARQ EXEHNGUESHER CGNTAINENG MULYBDENt M DISULFKDE Joe W. Stewart, Milwaukee, and Charles E. Bulloeh,

llrown Deer, Wis, assignors to Dov/smith Inc., Milwaukee, Win, a corporation of Delaware Filed Nov. 15, 1962, Ser. No. 237,879

9 Claims. (till. 200-120) This invention relates to a circuit interrupter and more particularly to an insulating member for confining an electric arc and extinguishing the same.

Circuit interrupters presently in broadest use are those having a fusible link, such as a fuse tube. Such a tube confines the electric are that is generated when the link fuses under overload conditions and interrupts the current. The fuse tube is formed of a material which is adapted to evolve an arc interrupting substance when subjected to the influence of an electric arc. Vulcanized or bone fiber or boric acid have been extensively used as the arc extinguishing material. However, both materials have disadvantages in that they are relatively hygroscopic, are subject to severe erosion under initial arcing conditions, have low physical strength, and are difficult to form or shape by molding.

The Wallace Patent 2,673,912 suggests the use of nylon as an arc extinguishing material. At low current values up to ampercs, nylon is stated to have a smaller loss in weight per half cycle of arcing :than other conventional materials such as bone fiber or boric acid. However, when dealing with high current values in the range of 1,060 to 12,800 ampcres, this trend is reversed, and it has been found that nylon has a larger loss in weight per half cycle of arcing than either bone fiber or boric acid. Further, in operating at these elevated current values the inner surface of a fuse tube constructed according to the teaching of Wallace becomes severely blistercd when subjected to a single arc. The blister-ed inner surface must be reamed to put the tube into operable condition again, and due to the extensive erosion of the inner surface, a second extinguishing cycle is frequently not possible.

'I he present invention is directed particularly to an insulating material for surrounding and confining an electric arc. The circuit interrupting member is generally formed of materials such as nylon, ethyl cellulose, polypropylene and polystyrene containing finely divided, dispersed particles of molybdenum disulfide, although other materials having arc extinguishing characteristics and in which molybdenum disulfide particles may be comp-atibly dispersed are acceptable. This combination of materials has been found. to rapidly develop a dense, heavy gas under electric arcing conditions. The gas thus generated completely extinguishcs the arc in an extremely short time period. With devices. set to interrupt at currents of from 1,000 to 12,000 amperes, a circuit interrupting member constructed in accordance with the invention will provide approximately extinguishing cycles, while a corresponding member formed of bone fiber will provide only 5 extinguishing cycle and one formed of nylon alone will provide only one.

It is presently believed that the molybdenum-disulfide which is dispersed in the arc extinguishing material acts catalytically in the decomposition of the extinguishing substrate under arcing conditions. The molybdenumdisulfide is thought to catalytically accelerate the rate of reaction of the extinguishing substrate caused by the are and to provide assistance in the extremely rapid and essentially complete production of a dense, non-conducting, arc extinguishing gas by the extinguishing substrate.

in addition to having improved arc interrupting and extinguishing characteristics, the circuit interrupting member of the invention has" greater physical strength Cit than presently available materials and has substantially reduced erosion tendencies. The increased physical stability of the resin member containing the molybdenum disulfidc is a decided improvement over other materials, such as bone fiber, which have appreciably greater ero' sion rates and, due to their hygroscopic nature, lack dimensional stability. Humidity changes are reflected by the substantial, and highly undesirable, expansion and contraction of the hygroscopic material.

Other objects and advantages will be appearing in the course of the following description.

The drawings illustrate the best mode presently contemplated of carrying out the invention.

in the drawings:

FIGURE 1 is a vertical section of a circuit interrupter embodying a fuse tube of the invention; and

FIG. 2 is an enlarged transverse section taken along line 2-2 of FIGURE 1.

The drawings illustrate a circuit interrupter comprising a generally cylindrical tube 1 provided with terminals 2 and 3 at its ends. The terminals 2 and 3 are connected by a replaceable fuse link illustrated generally at 4. Fuse link 4 comprises an upper terminal 5 having a threaded shank 6 which is received within a threaded opening in a button head 7. The button head 7 encloses the upper end of the terminal 2 and is secured thereto by a cap screw 8.

A strain wire 9 and a fusible element 10 are connected to the terminal 5 and the lower ends of the wires 9 and 10 are connected to a lower terminal 11 which is connected to the lower fuse tube terminal 3 by a flexible conducting lead 12. The conducting lead 12 is clamped to the lower terminal by a clamp 13 which is held in place by a screw 14.

According to the invention, the tube 1 includes an outer casing 15 and an inner liner 16, although the outer casing which provides additional insulation and strength may be eliminated in applications where such physical properties are not essential. The outer casing 15 which provides these increased properties for the tube, such as a high burst strength, may be formed of any non-conducting material such as fiber reinforced resin in which the fibrous material is impregnated with a thermosetting resin and wound in a generally helical pattern to provide the casing 15. The fiber reinforcement for the resin can take the form of glass or ceramic fibers, vegetable fibers, animal fibers, synthetic fibers or the like and the fibrous material may be in the form of continuously wound filaments, braided or woven materials, matting or the like.

The resin to be used in the outer casing 15 preferably is a thermosetting resin, such as an epoxy or polyester resin. The epoxy resins to be used are conventional types which may be prepared by condensing a polyhydric p-he- 1101 with a polyepoxide or a polyfunotio-nal halohydrin such as condensation product of epichloro-hydrin with b-isphenol as disclosed, for example, in Patent 2,801,227 entitled Process for Manufacture of Glycidyl Ethers of Polyhydric Phenols."

The liner 16 is formed of either a superpolyamide, such as nylon, or ethyl cellulose, polypropylene or polystyrene containing from about 0.1% to about 10l5% by weight of finely divided, dispersed particles of molybdenum disulfide. Other arc extinguishing materials in which molybdenum disulfide can be compatibly dispersed will provide acceptable circuit interrupting structures.

Nylon is a superpolymeric amide having a molecular weight of over 12,600 and is prepared from aliphatic dicarboxylic acids, such as adipic acid or sebacic acid, and aliphatic diarnines, such as hcxamethylenediamine, and is generally considered to have the following structure:

Ethyl cellulose is a cellulose plastic which may be pre pared by trcaling a form of cotton with caustic soda to give soda cellulose which is then reacted with ethyl chloride to yield ethyl cellulose flakes. The flakes may be treated with any of a variety of plasticizers to produce a material which may be extruded or molded. Ethyl cellulose has the formula: [C (H O) ],,C H

Polystyrene is polymer commonly classified as an ethenoid resin. It may be prepared by the catalytic combination of benzene with ethylene to give ethyl benzene which is dehydrogenated to produce a styrene monomer. The monomer is catalyzed by benzoyl peroxide and polymerization is carried out to produce polystyrene. Polystyrene has the formula: [C H CH:CH

Polypropylene is a polymer of the ethenoid resin class. It may be prepared by the polymerization of propylene. Polypropylene has the general formula: [CZ-I CH CH M.

The molybdenum disulfide is uniformly dispersed throughout the nylon, ethyl cellulose, polypropylene, polystyrene or other are extinguishing material in which it may be compatibly dispersed. The molybdenum disulfide may be mixed or incorporated with the base are mixing flakes or granules of the resin with molybdenum disulfide powder, or alternately by mechanically :mixing the flake or granular arc extinguishing material with a liquid dispersion of the molybdenum disulfide, after which the mixed materials can be dried. After incorporation of the molybdenum disulfide, the base are extinguishing material is melted and the tube liner 16 or other article may be formed by pressure molding, extruding, or any other desired technique.

To fabricate the fuse tube 1, the tubular liner 16 is disposed around a mandrel and fibrous material impregnated with an uncured thermosetting resin is then ap plied over the liner to provide the outer casing 15. After the desired thickness of reinforced material is applied, the composite structure is placed in an oven at a tornpcrature in the range of 300 F. to 350 F. for a period of about 55 to 65 minutes to cure the resin to an infusible state. To provide increased mechanical strength in the bond between the liner l6 and the outer casing 15, the outer surface of the liner 16 may be roughened or provided with knurls. ridges, serrations or the like. Suoh surface roughening acts to increase the available bonding surface area between the liner and the outer casing and to impart an additional degree of pushout resistance to the bond.

When the liner 16 is subjected to the high temperature of the are, it is believed that a reaction takes place during which the molybdenum-disulfide is thought to act catalyfieally to almost instantaneously produce a dense, heavy non-conducting arc extinguishing gas. This high velocity gas acts to physically disrupt the arc and to break the circuit maintained thereby. Due to the extreme rapidity of the circuit interruption, only a relatively small quantity of the arc extinguishing core material is dissociated into the gaseous state by the influence of the arc during fusion of the fusible material.

The combined dissociation of the surface elements of liner 16 subjected to the are is believed to act with extreme rapidity to interrupt the are produced by the fusion of the fusible link and to thereby break the circuit established by the arc. Due to the rapidity of the interruption, only small material losses at the inner surface of liner 16 are experienced by the fuse tube thereby permitting repeated reuse of the tube as a circuit interrupting device.

Utilizing an arc extinguishing liner 16 comprising 97.5% nylon and 2.5% molybdenum disulfide as many as 20 separate arcs were extinguished "with one liner. This is due primarily to the rapid extinction of the arc with the resultant relatively small erosion loss of the liner material during any one arcing. In contrast to a bone fiber fuse tube which can be expected to provide 5 are extinguishing cycles and a nylon fuse tube which can be expected to provide only a single are extinguishing cycle in the range of 1,000 to 12,000 amperes, it is apparent that the fuse tube of the instant invention affords a tremendous economic advantage in the arc extinguishing held.

The base circuit interrupting substance containing the particles of molybdenum disulfide provides a circuit interrupting material which will withstand a substantially greater number of arcings than conventional materials at currents in the range of 1,000 to 12,000 amperes before being appreciably eroded. Furthermore, the material, when compared to materials which are presently in common use, is relatively non-hygroscopic thereby providing a circuit interrupting material with substantially increased dimensional stability which will, therefore, not expand and shrink to any appreciable degree with widely varying humidity conditions.

The are extinguishing material is particularly adaptable for use as a liner in devices which employ an outer casing formed of reinforced thermosetting resin. After winding or laying up of the resin impregnated fibers to form the outer casing 15, the composite structure can be heated to temperatures in the range of 300 F. to 350 to cure the epoxy resin without decomposing or otherwise affecting the composition of the liner. This increases the overall speed of fabrication of the present fuse tube over a tube using bone fiber, in that bone fiber decomposes at temperatures below this range, and therefore the curing temperature for the resin of the outer casing must be maintained below this range thereby increasing the length of curing time.

While the above description is directed to a fuse tube, such as that used with a transformer in power lines, it is contemplated that the base are extinguishing material containing the particles of molybdenum disulfide can be used in any are extinguishing apparatus, such as exhaust blast blocks, lightning arresters, are chutes, arc shields, oil reclosures, transformer protective devices, and heavy duty switch components, and may take the form of sheets, blocks or the like.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. A circuit interrupting device having an arc confining wall, the wall including the materials molybdenum disulfide and an arc extinguishing substance being physically compatible with the molybdeum-disulfide, and means provided adjacent the wall for producing an arc, the material of the wall effecting extinction of the are.

2. In a circuit interrupting apparatus, means for forming an arc and an arc extinguishing member consisting essentially of about 0.1% to about 15% by weight of molybdenum disulfide and an arc extinguishing substance being physically compatible with the molybdenum disulfide disposed in arc extinguishing proximity to the path of the are.

3. An are extinguishing apparatus comprising means for establishing an arc and an arc extinguishing member consisting essentially of about 0.1% to 15% by weight of molybdenum disulfide and the balance being a material selected from the group consisting of superpolyamides, ethyl cellulose, polypropylene, and polystyrene being disposed along the path of the are and in arc extinguishing proximity thereto.

4. In an arc extinguishing apparatus for use in a circuit interrupter having means for producing an are, an are extinguishing conduit adapted to be disposed around the are producing means and the path defined by the are to confine and extinguish an are produced thereby consisting essentially of about 0.1% to 15% by weight of molybdenum disulfide and the balance being a substance selected from the group consisting of superpolyamide resins, ethyl cellulose, polypropylene, and polystyrene, the molybdenum disulfide "being dispersed as finely divided particles throughout said substance, and a reinforcing structure secured to the exterior of the conduit to resist pressures evolved by the confined are.

5. An arc extinguishing and confining fuse tube for use in a circuit interrupter having a fusible link which may be fused to form an arc consisting essentially of about 0.1% to 15% by weight of molybdenum disulfide and the balance being nylon and adapted -to be disposed in arc extinguishing proximity to the fusible link 6. An arc extinguishing and confining fuse tube for use in a circuit interrupter having a fusible link which may be fused to form an arc consisting essentially of about 0.1 to 15% by weight of molybdenum disulfide and the balance being ethyl cellulose and adapted to be disposed in arc extinguishing proximity to the fusible link.

7. An arc extinguishing and confining fuse tube for use in a circuit interrupter having a fusible link which may be fused to form an arc consisting essentially of about 0.1% to 15 by weight of molybdenum disulfide and the balance being polypropylene and adapted to be disposed in arc extinguishing proximity to the fusible link.

8. An arc extinguishing and confining fuse tube for use in a circuit interrupter having a fusible link which may be fused to form an arc consisting essentially of about 0.1% to 15% by weight of molybdenum disulfide and the balance being polystyrene and adapted to be disposed in arc extinguishing proximity to the fusible link.

9. An arc extinguishing apparatus for use in a circuit interrupter, comprising an outer reinforcing member, an inner arc extinguishing and confining member consisting essentially of a dispersion of molybdenum disulfide particles in a gas forming arc extinguishing substance, and a replaceable fuse link including a fusible portion located adjacent the arc extinguishing member, the fusible portion rupturing in response to a predetermined current passing therethrough to establish an electrical arc, the are causing the arc extinguishing member to evolve a heavy, dense gas capable of quickly disrupting the are thereby breaking the circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,609,470 Quinn Sept. 2, 1952 2,673,912 Wallace Mar. 30, 1954 2,855,377 Stott Oct. 7, 1958 3,002,072 Nava et a] Sept. 26, 1961 3,021,409 Cobine et a1 Feb. 13, 1961 

1. A CIRCUIT INTERRUPTING DEVICE HAVING AN ARC CONFINING WALL, THE WALL INCLUDING THE MATERIALS MOLYBDENUM-DISULFIDE AND AN ARC EXTINGUISHING SUBSTANCE BEING PHYSICALLY COMPATIBLE WITH THE MOLYBDENUM-DISULFIDE, AND MEANS PRO- 